Hi, this is not a complicated tutorial like others, but maybe some people will find this useful. If you send a gmail that has typos or you regret that you sent it or I don't know, maybe you changed your mind, it is an option that will delete the message if the person you have sent it to didn't read it.

To do this:

1. Click the gear in the top right.
2. Select Settings.
3. Click the Labs tab.
4. Find the "Undo Send" lab and select the Enable radio button.
5. Click Save Changes at the bottom of the page.
6. Select the amount of time you have to undo sending a message by clicking the gear icon , and finding the "Undo Send:" section in the General tab of your Settings.

Credits does not go to me for this tutorial, but still, if it will help atleast one person here it's still a good share :)